Powertrain Controls - ECM/PCM

Pressure Switch Manifold Fault Circuit:

Circuit Description:
The Pressure Switch Manifold (PSM) consists of five pressure switches combined into one unit and mounted on the valve body. The PCM/TCM supplies battery voltage to the PSM on three separate wires. By grounding one or more of these circuits through various combinations of the pressure switches, the PCM/TCM detects what gear range has been selected by the vehicle operator.

Pressure Switch Manifold Fault Diagnostic Chart:

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test compares the indicated range to the range actually selected.

2. This test checks for correct voltage from the PCM/TCM to the transmission pass-thru connector.

3. This final test will detect a short to ground in any one of the three PSM range circuits.


Diagnostic Aids:
Code 28 will set if the PCM/TCM detects one of two "illegal" PSM combinations.

Expected Voltage Readings:

See accompanying chart for various combinations. Be sure to check pass-thru connector for good contact.